1. Field of the Invention
The present invention relates to a sealed prismatic battery, and particularly to a prismatic rechargeable battery module consisting of a plurality of cells with lower internal resistance.
2. Description of Related Art
One known rechargeable battery module consisting of a plurality of cells to achieve required power capacity has the following structure: The plurality of prismatic cells are arranged in parallel, with their longer lateral walls in contact with each other, and united by restraining bands together with end plates placed on the outer sides of the cells at the either end. Leads extending from the top ends of electrode plates of the cells upwards are connected to terminals mounted in the lid of the battery case, and these terminals of the cells are connected to each other via connection plates.
The cells are connected via a long connection path with many connection parts in this battery, resulting in large components' resistance. In fact, the proportion of the components' resistance in such a battery to reaction resistance caused by the reaction between positive and negative electrode plates and liquid electrolyte in the battery was as high as 40 to 50%, and the high heat generation because of the large internal resistance was a major barrier to the realization of higher power output or improvement in battery life. There was also the problem of high costs because of the large number of components required for the complex connection structure of the cells.
In view of this, the applicants of the present invention have proposed a sealed prismatic battery 101 containing a plurality of cells 102 shown in FIG. 4 and FIG. 5. The battery 101 has a flat prismatic battery case 103 made of prismatic cell cases 104, which have short lateral walls and long lateral walls, of serially arranged cells 102. These cells are connected together in such a manner that their short lateral walls are used as partition walls 105 between the cells. The open top ends of the cell cases 104 are closed by an integral lid 106. Connection holes 107 are formed in the short lateral walls of the cell cases 104 at the far ends and in an upper part of each partition wall 105. Each cell case 104 constitutes a cell 102, accommodating liquid electrolyte and an electrode plate group 108 consisting of stacked-up rectangular positive and negative electrode plates and separators interposed in between them. Lateral edges on one side of the alternately stacked-up positive and negative electrode plates are protruded in opposite directions to form positive and negative leads 109a, 109b, respectively, to which collector plates 110a, 110b are connected by welding or the like.
In an upper part of the collector plates 110a, 110b is protruded a connection boss 111 which fits into the connection hole 107. The connection bosses 111 of positive and negative collector plates 110a, 110b are connected together by welding between adjacent cell cases 104. In the connection holes 107 in the end faces of the cell cases 104 at either far end are fitted positive and negative connection terminals 112 with connection bosses 113, respectively, and these connection bosses 113 are each connected to the connection bosses 111 of positive and negative collector plates 110a, 110b by welding. The plurality of cells 102 are thus connected in series in the battery case 103 such as to output power via the connection terminals 112 at both ends.
In this structure, the connection terminals 112 are disposed at the upper part of the end walls of the battery case 103, their connection bosses 113 being bonded to the upper part of the collector plates 110a, 110b. Consequently, the connection arrangement between the collector plates 110a, 110b and the electrode plate group 108 welded together at a plurality of bonds 116 located at suitably spaced intervals along the length of the collector plates results in uneven current distribution in the electrode plate group 108 due to the small cross section and large resistance of the collector plates 110a, 110b. As illustrated by white arrows in FIG. 6, the amount of current flowing from the connection terminal 112 through the collector plate 110a via the bonds 116 into the electrode plate group 108 is larger at bonds 116 nearer to the connection terminal 112 and smaller at bonds farther from the connection terminal. As a result, the electrode plate groups 108 cannot exhibit their power generating properties uniformly, causing considerable power loss.
What is worse, there is a problem of high internal resistance caused by the connection arrangement of the collector plates 110a, 110b facing each other via partition walls 105. That is, despite the relatively short current flow path from the positive and negative electrode plates to the collector plates 110a, 110b, the internal resistance is relatively high, since the collector plates 110a, 110b are welded together at one location at the tips of their respective connection bosses 111 at the top. This connection arrangement also causes uneven current distribution in the electrode plate groups 108 because of the differing distances from the connection points at the top to respective bonds 116. As a result, the electrode plate groups 108 cannot exhibit their power generating properties uniformly, causing considerable power loss.